Upconverting Nanoparticles for Security Applications
2016
Upconversion (UC) is a nonlinear process in which the excitation energy is
absorbed by two or more photons that leads to the emission of light at shorter
wavelength than the excitation wavelength. In this case, near-infrared (NIR)
light, that is, 980 nm (lower energy, longer wavelength) is upconverted to
visible light, 400-700 nm (higher energy, shorter wavelength) by UC material. In contrast to other emission processes, UC has high internal quantumCONTENTS10.1 Introduction 291
10.2 Upconverting Nanoparticles 292
10.3 Upconversion Security Printing Prospective 293
10.4 Synthesis, Functionalization, and Scale-up 29810.4.1 Hansen Solubility Parameters 299
10.5 Toxicity Assessment 299
10.6 Security Printing Applications 30110.6.1 Red, Green, and Blue Upconversion Printing 302
10.6.2 Micro Upconverting QR Code Tags 304
10.6.3 Color-Coded Multilayer Photopatterned Microstructures ......305
10.6.4 Micro Barcodes 305
10.6.5 Tunable Lifetime Multiplexing of UCNPs 305
10.6.6 NIR-to-NIR Upconversion Security Printing 308
10.6.7 Scanning Laser Imaging of Upconversion Printing 312
10.6.8 Multicolor Nano Barcoding in a SingleUpconversion Crystal 313
10.6.9 Upconversion Polymeric Nanobers 31410.7 Readability of Upconversion Prints 314
10.8 Conclusion 315
Acknowledgments 316
References 316efciency (Haase and Schafer 2011). In the 1950s, the UC effect was rst discovered and studied intensively during the 1960s but up until 2003 it was
observed only in bulk, transition metals or rare earth-doped phosphors
which were suggested to have applications in the eld of detectors, display,
and laser materials (Bunzli and Eliseeva 2011). Since then UC materials have
found their application in solar cells, waveguide ampliers and later, they
became applicable in rewritable optical storage nondestructive optical memory and many more potential scientic applications; and in the last decade,
UC materials became well known in the biological eld for bio sensing, drug
delivery, etc. (Ho et al. 2003; Kim et al 2009; Shalav et al. 2005; Suyver et al.
2005; Vennerberg and Lin 2011; Wang and Bass 2004; Wang and Liu 2009;
Wang et al. 2010; Zhou et al. 2015).
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